Izzy, you have received some great advice and perspective in the above posts, I hardly need to add any.

I will simply mention that the dying process of a parent is an extremely stressful event for all family members. Everyone's emotions are raw now, people are tired and sad, and ancient hurts and grievances bubble up to the surface. Thank goodness for Hospice!

As your mother's life reaches closure, perhaps this would be a good time for you to reach closure regarding your sister's and your mother's relationship. It won't help your health or your heart to carry around such negative feelings, and I imagine your mother would far prefer that her daughters would carry on after her death in the spirit of forgiveness and support.